I did a project recently and used the advanced 3D and crosshatch and perimeter options where the gimbal goes to 65 degrees. I know this improves the 3D aspect of the model, but will my 2D ortho be of poor quality because it’s not 90 degrees or is quality for the orthomap still good? I want to use the digital terrain maps as well. Will not having pure nadir shots affect this?
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Your model will look really crisp which will make the ortho map look better but ground elevations may suffer a little. Introducing oblique angles only complicates the reconstruction and it becomes hard to see low spots and in between objects. Personally I always include nadir images so that I can process them separately if I really need good terrain as well. We then use a point cloud editor to separate the structures from their point cloud and insert them into the DTM.
Thanks! How much do you think the elevations will suffer? This is going to be used to plan a landscaping project
It really depends on the specific site configuration as to how much the ground will suffer. All I know is that if you are looking for 3cm accuracy you’re not going to get it with obliques. Some areas may be good, others close and still other 5-10cm off. It all has to do with the perspective of the camera and the inability to see through things.
Imagine flying over a field that has a fair amount of vegetation. With a nadir angle you can see down in between and which allows processing to find true low points. With an oblique angle this is not possible when there is constantly a chute of grass or bushing blocking that low spots. Or trying to get good values in between buildings. Not going to happen with obliques alone.
Thanks for the information. That is very helpful. I’m brand new to the digital terrain model stuff. Rather than starting a new discussion, if you don’t mind me asking on here, how do I interpret the elevation data? When I click on the elevation and then terrain only it gives me a range of numbers on the bottom and colors above. Do those numbers represent the range of heights of the terrain above sea level? The one I just did today the lowest number is a small negative number so I’m confused as to what exactly I’m looking at.
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Yes, it is just a gradient to help visualize the elevations. You can move the slider to change the range which comes in handy if you want to isolate a smaller area of the map and get better definition on the area. It also helps if you have a map with large elevation changes. It becomes to see good detail because the values are so spread out.
The elevations represent what you used as control. If no control then the drone is the control and you will get the HAE (Height Above Ellipsoid). If you have surveyed GCP’s they will most likely have orthometric (ground) elevations. You get to ground by adding/subtracting the Geoid separation from the ellipsoid. You can Google any of these terms or even this forum to start getting a grasp of the different datums.
If you see negative numbers then you must be close to a coast and the ellipsoid goes above the ground.